1. Field of the Invention
The invention relates to carbon-based composites, and in particular to carbon-based composites derived from phthalonitrile resins.
2. Description of the Related Art
Carbon-based composites are materials that are composed of a fibrous reinforcement in a carbonaceous or graphitic matrix. A filler or coating may also be included to impart specialized properties.
As used in this application, the term "carbon-based composite" refers generally to any composite having a fibrous reinforcement in a carbonaceous or graphitic matrix. The terms "carbon/carbon composite" or "carbon-carbon composite" refer to a carbon-based composite wherein the fibrous reinforcement comprises carbon fiber.
Carbon-carbon composites are lightweight materials, with densities ranging from about 1.36 to about 2.00 g/cm.sup.3, depending on the precursors used for their production. Carbon-based composites may have greater density, depending on the density of the particular fibrous reinforcement used. Carbon-based composites possess great thermal stability in non-oxidizing environments and may be coated with an oxidation-resistant coating for use in oxidizing environments.
Typically, carbon-based composites are formed by impregnating a fibrous material with an organic resin and then heating or pyrolyzing the mixture to carbonizing temperatures. For carbon/carbon composites, the carbon fiber material is typically derived from polyacrylonitrile (PAN), rayon, or petroleum pitch. Silicon carbide, metal, glass or ceramic fibers may be used to fabricate other types of carbon-based composites.
First-generation matrix materials for carbon-based composites were derived from phenolic and phenolic-furfuryl alcohol resins. These resins have the disadvantage that when they are cured and pyrolyzed to form a carbon-based composite, they generate volatiles, which create voids in the composite. To eliminate the voids and to produce a carbon-based composite with an acceptable density, multiple steps of impregnation and carbonization are required. The process of making a carbon-based composite with these types of resins is therefore time-consuming and expensive. With some currently used carbon precursor materials, it can take 6 to 8 months of repeated impregnation and pyrolysis steps to make a thick, complex carbon/carbon structure. More recently, other materials such as liquid (mesophase) pitch have been used as the matrix material. These materials typically have a high viscosity, which makes the process of impregnating a fibrous material more difficult. Other processes such as chemical vapor deposition/chemical vapor infiltration (CVD/CVI) of volatile hydrocarbon compounds have been used to achieve higher densities. However, with chemical vapor methods, carbon tends to deposit preferentially on the surface of the fibrous material and a thorough penetration of a thick fiber matrix is difficult to achieve.
A variety of methods and materials for making carbon/carbon composites are described in numerous publications and patents including, for example, the following: Buckley, John D. and Edie, Dan D., ed., Carbon-Carbon Materials and Composites, Noyes Publications, Park Ridge, N.J. (1993); Delmonte, John, Technology of Carbon and Graphite Fiber Composites, Van Nostrand Reinhold Company, New York, N.Y. (1981); Schmidt et al, "Evolution of Carbon-Carbon Composites (CCC)" SAMPE Journal, Vol.32, No. 4, July/August 1996, pp 44-50; "Expanding Applications Reinforce the Value of Composites" High Performance Composites 1998 Sourcebook; U.S. Pat. No. 3,914,395 to Finelli, et al; U.S. Pat. No. 4,178,413 to DeMunda; U.S. Pat. No. 5,061,414 to Engle; U.S. Pat. No. 4,554,024 to Zimmer, et al; and U.S. Pat. No. 5,686,027 to Olsen, et al. All of the above patents and publications are incorporated herein by reference.
A method for making a silicon carbide fiber reinforced carbon composite is described in U.S. Pat. No. 5,759,688 to Lee et al, incorporated herein by reference.
Phthalonitrile monomers and resins have been used for making thermoset polymers. Phthalonitriles have the advantage that they are easily processed and can be cured without generating volatile by-products. Various phthalonitrile resins are described, for example, in U.S. Pat. No. 3,730,946, U.S. Pat. No. 3,763,210, U.S. Pat. No. 3,787,475, U.S. Pat. No. 3,869,499, U.S. Pat. No. 3,972,902, U.S. Pat. No. 4,209,458, U.S. Pat. No. 4,223,123, U.S. Pat. No. 4,226,801, U.S. Pat. No. 4,234,712, U.S. Pat. No. 4,238,601, U.S. Pat. No. 4,259,471, U.S. Pat. No. 4,304,896, U.S. Pat. No. 4,307,035, U.S. Pat. No. 4,315,093, U.S. Pat. No. 4,351,776, U.S. Pat. No. 4,408,035, U.S. Pat. No. 4,409,382, U.S. Pat. No. 4,410,676, U.S. Pat. No. 5,003,039, U.S. Pat. No. 5,003,078, U.S. Pat. No. 5,004,801, U.S. Pat. No. 5,132,396, U.S. Pat. No. 5,159,054, U.S. Pat. No. 5,202,414, U.S. Pat. No. 5,208,318, U.S. Pat. No. 5,237,045, U.S. Pat. No. 5,242,755, U.S. Pat. No. 5,247,060, U.S. Pat. No. 5,292,854, U.S. Pat. No. 5,304,625, U.S. Pat. No. 5,350,828, U.S. Pat. No. 5,352,760, U.S. Pat. No. 5,464,926, U.S. Patent Application by Satya B. Sastri and Teddy M. Keller for "FIBER-REINFORCED PHTHALONITRILE COMPOSITE CURED WITH LOW-REACTIVITY AROMATIC AMINE CURING AGENT" filed Oct. 2, 1997 and U.S. Patent Application by Satya B. Sastri and Teddy M. Keller for "PHTHALONITRILE THERMOSET POLYMERS AND COMPOSITES CURED WITH HALOGEN-CONTAINING AROMATIC AMINE CURING AGENTS" filed Oct. 2, 1997. All of these patents and applications are incorporated herein by reference.
U.S. Pat. No. 4,587,325, incorporated herein by reference, describes a conductive phthalonitrile polymer formed by heating a mixture of a diether-linked bisorthonitrile (phthalonitrile) monomer and an amine to a temperature above 450.degree. C. U.S. Pat. No. 5,389,441, incorporated herein by reference, describes a fiber-reinforced composite formed by combining a fiber sized with a cured or partially cured phthalonitrile coating and a polymeric matrix. U.S. Pat. No. 5,645,219, incorporated herein by reference, describes the use of phthalonitrile resin as a matrix material in a fiber-reinforced ablative composite. The patent describes thermogravimetric testing of cured neat phthalonitrile resin samples by heating to 900.degree. C. Methods of making fiber-reinforced thermoset composites based on phthalonitrile resins are described in Sastri et al, "Phthalonitrile-Carbon Fiber Composites" Polymer Composites, December 1996, Vol. 17, No. 6, pp 816-822 and Sastri et al "Phthalonitrile-Glass Fabric Composites", Polymer Composites, February 1997, Vol. 18, No. 1, pp 48-54, the disclosures of which are incorporated herein by reference.